The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicles include an internal combustion engine that generates drive torque. More specifically, an intake valve is selectively opened to draw air into cylinders of the engine. The air mixes with fuel to form an air/fuel mixture that is combusted within the cylinders. The air/fuel mixture is compressed and combusted to drive pistons within the cylinders. An exhaust valve selectively opens to allow the exhaust gas resulting from combustion to exit the cylinders.
A rotating camshaft regulates the opening and closing of the intake and/or exhaust valves. The camshaft includes cam lobes that are fixed to and rotate with the camshaft. The geometric profile of a cam lobe determines a valve lift schedule. More specifically, the geometric profile of a cam lobe controls the period that the valve is open (duration) and the magnitude or degree to which the valve opens (lift).
Variable valve actuation (VVA) technology improves fuel economy, engine efficiency, and/or performance by modifying a valve lift event, timing, and duration as a function of engine operating conditions. Two-step VVA systems include variable valve lift mechanisms, such as hydraulically-controlled, switchable roller finger followers (SRFFs). A SRFF associated with a valve (e.g., the intake or exhaust valves) allows the valve to be opened in two discrete lift states: a low lift state and a high lift state.
A control module selectively transitions the SRFF mechanism between the high and low lift states based on demanded engine speed and load. In other words, the control module controls which camshaft lobe will contact the SRFF mechanism and control opening and closing of the associated valve. For example, the control module may transition the SRFF mechanism to the high lift state when the engine speed is greater than a predetermined speed, such as approximately 4,000 revolutions per minute (rpm). Operating in the high lift state under such conditions may aid in avoiding potential hardware damage.